For gaskets used in fuel cells, secondary batteries, condensers, etc., rubber materials are widely used. Seal materials for these applications are much used for stacking a large number of cells one upon another, and the stacked products themselves, e.g. fuel cells, secondary batteries, condensers, etc. can be reduced in size by use of seal, materials as thin as or as narrow as possible.
As to thin seals for these applications, a gasket (JP-A-9-231987, JP-A-7-263004, JP-A-7-226220, JP-A-7-153480, etc.) and a gasket comprising a rubber sheet and a foamed sponge layer disposed thereon (JP-A-312223) have been proposed, but all of these thin seals are not directed to satisfying such requirements as reduction in thickness of seals, prevention of positional alignment failure during the assembling, reduction in specific pressure, specific pressure uniformalization, etc., and are hard to satisfy, if any, all these requirements.
That is, the ordinary separated type gaskets can satisfy only the reduction in specific pressure, specific pressure uniformalization, etc. but fails to satisfy reduction in thickness of seals, positional alignment failure during the assembling, etc. at the same time.
When the rubber hardness is high in case of stacking a large number of unit cells one upon another, tightening force of seal is liable to become uneven locally or depending on stacking positions, and thus a low rubber hardness is required for the rubber seal materials.
When the rubber seal materials are thin or narrow, or low in hardness, the seal materials themselves become so limp and soft, that it is difficult to mount the seals on the seal positions exactly and rapidly during the cell assembling and liable to cause a sealing failure in the stacked products.
To improve handling of seal materials, a somewhat hard and thin substrate, e.g. a stainless steel sheet (SUS grade), whose one side or both sides are integrally molded with a thin or narrow low-hardness rubber seal, is used, and such a substrate-integrated seal never undergoes considerable sagging when its one end is picked up and thus can be mounted on the desired position exactly, thereby facilitating the cell assembling work.
However, such integration of the substrate with rubber requires an additional adhesive to bond the substrate to the rubber, and thus an additional coating step and a drying step of the adhesive are required, resulting in a cost increase. Furthermore, components of the adhesive are partially extracted into the electrolytic solution, etc. with a risk of contamination of the electrolytic solution or catalysts.
Furthermore, from the viewpoints of performance or life of cells (including fuel cells and secondary batteries), condensers, etc., materials incapable of contaminating liquids to be used in the cells, etc. such as electrolytic solution, etc. or catalyst for promoting the reaction, etc. (e.g. a catalyst layer of platinum, etc. present on both sides of an electrolyte membrane or in the electrolyte membrane) are required as the materials for use in the cells or condensers.
Less harmful extractable components and no contamination are required for seal materials for use in the cells or condensers, so that the seal material components may not give no adverse effect at all on the cells or condensers, particularly in case of fuel cells, contamination, if any, of catalyst (Pt) with extracted components from cell member can decrease power generation performance, leading to risks such as a failure of stable power supply.
Furthermore, in case of fuel cells, the electrode plates, solid electrolyte membranes, separating plates, etc. are fastened by compression, and thus a smaller reaction force is require, during the fastening. In the fuel cells, it is necessary that the electrolyte membrane must be always wet and thus extractable components from the seal material into water supplied to keep the wet state or into water formed by reaction of hydrogen with oxygen (the electrolytic solution) must be less.